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California Drought: What's the Latest?

California Drought: What's the Latest?

17 December 2014

ANALYSIS - California is currently experiencing its worst drought since the 1970s. With much of the state now flooding, Gemma Hyland asks: Is it enough to end the dry spell?

A high pressure ridge off the West Coast (typical of historic droughts) prevailed for three winters, blocking important wet season storms, with ocean surface temperature patterns making such a ridge much more likely.

california droughtTypically, the winter season in California provides the state with a majority of its annual snow and rainfall that replenish water supplies for communities and ecosystems.

According to the National Weather Service, multiple Pacific systems moving inland will allow the much needed wet pattern to continue across the western US, especially for the extreme drought-stricken California.

Surges of moisture with each approaching system, combined with orographic effects, should produce periods of moderate to heavy rains along the California coast and beneficial snowfall accumulations are expected to pile up along the Sierra Nevada range.

"It's important to note that California's drought, while extreme, is not an uncommon occurrence for the state.

"In fact, multi-year droughts appear regularly in the state's climate record, and it's a safe bet that a similar event will happen again.

"Thus, preparedness is key," said Richard Seager, professor with Columbia University's Lamont Doherty Earth Observatory.

Drought Monitor

usda drought monitor

Locally heavy precipitation fell across portions of the state this past week. Amounts ranged from 1-6 inches (liquid equivalent) across a large portion of northern California, and parts of the central and southern coastal areas.

Up to 3 inches of precipitation (liquid equivalent) was reported in the southern Sierras. However, snow pack remains well below-normal in many areas due to the relatively mild temperatures associated with these storm systems.

california droughtIn addition, much more precipitation is needed to replenish lost reservoir storage. There are still deficits in the conservation pool of millions of acre-feet in the Shasta and Oroville reservoirs north of Sacramento.

Oroville reservoir gained about 100,000 acre-feet of storage in the recent storm, returning to one million acre-feet in storage capacity. The capacity of this reservoir is 3.5 million acre-feet, with a flood reserve space of 750,000 acre-feet.

Well to the south, last week’s storm produced several inches of rain for San Luis Obispo, Santa Barbara, Ventura, and Los Angeles Counties.

However, this was not enough to generate runoff in natural streams and therefore did not provide any benefit to surface reservoirs. Since the start of the Water Year (October 1), almost all precipitation gauges in the area are still running below normal.

No revisions were made to the California drought depiction this week. With the anticipation of another significant precipitation event in the short-term, alterations could be required next week, pending resulting impacts.

Gemma Hyland, Editor

Gemma Hyland, Editor

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